1. Field of the Invention
The present invention relates to a sheet processing apparatus for aligning a side edge of a sheet and to an image forming apparatus having the sheet processing apparatus in an apparatus main body.
2. Description of the Related Art
Hitherto, as an image forming apparatus for forming an image onto a sheet, there is a type in which a sheet processing apparatus for aligning a sheet side edge along a sheet conveying direction is provided for an apparatus main body (the Official Gazette of Japanese Patent Application Laid-Open No. 2005-306506).
Schematic diagrams of a sheet processing apparatus in the related art are illustrated in FIGS. 16A to 16C and 17A to 17C. The sheet processing apparatus has a processing roller 204 as a moving unit. The processing roller 204 is brought into contact with an upper surface Sb of a sheet S stacked on a processing tray 205 as a stacking unit so that the processing roller can slip and is moved in a sheet width direction (direction illustrated by an arrow) which crosses a sheet ejecting direction. While moving in the arrow direction, the processing roller 204 moves the sheet in the arrow direction so that a side edge Sa of the sheet S is come into contact with a width restricting plate 239 as a side edge aligning unit, thereby making a side edge alignment of the sheet. The side edge Sa of the sheet S indicates a sheet edge along the sheet conveying direction.
When the side edge alignment of the sheet is made, the processing roller 204 slip-moves (slips) on the sheet in a state where the side edge Sa of the sheet S is in contact with the width restricting plate 239 and causes a deflection in the side edge portion of the sheet, thereby raising side edge aligning precision of the sheet.
The sheet processing apparatus in the related art uses what is called a center-main conveyance in which the sheet is conveyed in a state where a center in the width direction of the sheet and a center in the width direction of a sheet conveying path are made coincident. A center (CL1) in the width direction of the processing roller 204 existing at a home position also coincides with a center (CL2) in the width direction of the sheet.
Therefore, a distance (L2) between the side edge Sa of the sheet having a large width size in FIGS. 17A to 17C and an edge surface 204a of the processing roller 204 is longer than a distance (L1) between the side edge Sa of the sheet having a small width size in FIGS. 16A to 16C and the edge surface 204a of the processing roller 204.
A distance (L8) at which the processing roller 204 moves from the center (CL2) in the width direction of the sheet to a position where the processing roller 204 finishes the side edge alignment of the sheet and stops, is set to a predetermined value irrespective of the width size (length in the arrow direction) of the sheet. Therefore, an interval (L5) between the processing roller 204 and the width restricting plate 239 at the time when the processing roller 204 finishes the side edge alignment of the sheet and stops, is constant irrespective of the width size of the sheet.
Consequently, in the case of the sheet having the large width size, a distance at which the processing roller 204 further moves (alignment slip movement) after the processing roller 204 makes the side edge Sa of the sheet hit to the width restricting plate 239 is equal to L2−L5 (=L7). In the case of the sheet having the small width size, a distance at which the processing roller 204 further moves (alignment slip movement) after the processing roller 204 made the side edge Sa of the sheet hit to the width restricting plate 239 is equal to L1−L5 (=L6). Since L2>L1, L7>L6.
That is, the alignment slip movement distance of the processing roller 204 in the case of the sheet having the large width size is larger than that of the sheet having the small width size.